The present invention relates generally to disk drive systems and in particular to control techniques for performing seek operations in a disk drive.
A seek operation is an operation wherein a magnetic head or heads in a magnetic disk drive are moved to a predetermined position or positions on the magnetic disk media. Modern magnetic disk drives contain several tens of thousands of tracks which collectively constitute a storage area. The tracks are formatted in a concentric manner and provided on a magnetic disk medium in order to achieve high density storage of information for increased storage capacity.
Magnetic disk drives can perform random access at high speeds. Information is scattered about the disk in units called blocks and is randomly accessible for reading. Likewise, writing of information can occur at randomly selected locations. Much effort has been expended to increase speed of seek operation so as to shorten the average access time, with a view to improving the performance of magnetic disk drives. The increasing use of computer systems such as notebook-sized personal computers, household desktop computers and so on, have placed ever heavier demands for additional cost reduction in magnetic disk drives and for improvements in magnetic disk drive operation. One area of demand is improvement in seek time while maintaining low vibrational noise in the disk drive.
A seek operation includes moving the read/write head from one location to another. The notion of “seek span” refers to the number of tracks to be traversed by the read/write head during a seek operation. The term “span distance” will also be used in this application to refer to the number tracks to be traversed by the read/write head. The head is accelerated and decelerated by driving an actuator at appropriate times to position the head at the correct track. A voice coil motor (VCM) is driven by current to operate the actuator. Acceleration of the actuator is produced by driving the VCM with current of a first sign (e.g., a positive current), while deceleration of the actuator is initiated by driving the VCM with a current of the opposite sign (e.g., a negative current). The activity of acceleration and deceleration produce mechanical vibrations (noise) in the system which is detrimental to operation of the system. It is therefore desirable to reduce such noise.